Systems and methods for network access control

ABSTRACT

Provided are methods and systems for network access control. A method for network access control may commence with determining whether a client device is a trusted source or an untrusted source. The determination may be performed using a SYN packet received from the client device. The SYN packet may include identifying information for the client device. When it is determined that the client device is neither the trusted source nor the untrusted source, the method may continue with transmitting a SYN/ACK packet to the client device. The SYN/ACK packet may include a SYN cookie and identifying information for a network device. The method may further include receiving an ACK packet from the client device that may include the identifying information for the client device, identifying information for the network device, and the SYN cookie. The method may continue with establishing a connection with a network for the client device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation and claims the prioritybenefit of U.S. Nonprovisional patent application Ser. No. 15/799,528,filed on Oct. 31, 2017, entitled “SYSTEMS AND METHODS FOR NETWORK ACCESSCONTROL”, which is a continuation of U.S. Nonprovisional patentapplication Ser. No. 14/261,322, filed on Apr. 24, 2014, now U.S. Pat.No. 9,838,425, entitled “SYSTEMS AND METHODS FOR NETWORK ACCESSCONTROL”, which claims the priority benefit of U.S. ProvisionalApplication Ser. No. 61/816,099, filed on Apr. 25, 2013, which arehereby incorporated by reference herein in their entirety, including allreferences cited therein.

FIELD OF THE INVENTION

The present disclosure relates generally to data processing, morespecifically to security mechanisms that may be employed by anApplication Delivery Controller (ADC) to facilitate network accesscontrol and prevent malicious attacks such as a denial of serviceattack.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described in the Detailed Descriptionbelow. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

The present disclosure relates to approaches for network access control.Specifically, a system for network access control may include a networkdevice and a memory communicatively coupled to the network device. Thenetwork device may be configured to determine whether a client device isa trusted source or an untrusted source for a network. The determinationmay be performed using a SYN packet received from the client device. TheSYN packet may include identifying information for the client device.Based on the determination that the client device is neither the trustedsource nor the untrusted source, the network device may transmit aSYN/ACK packet to the client device. The SYN/ACK packet may include aSYN cookie and identifying information for the network device. Thenetwork device may be further configured to receive an ACK packet fromthe client device that may include the identifying information for theclient device, identifying information for the network device, and theSYN cookie. The network device may be further configured to establish aconnection with the network for the client device.

According to another approach of the present disclosure, there isprovided a method for network access control. The method may commencewith determining, at a network device, whether a client device is atrusted source or an untrusted source for a network. The determinationmay be performed using a SYN packet received from the client device. TheSYN packet may include identifying information for the client device.When it is determined that the client device is neither the trustedsource nor the untrusted source, the method may continue withtransmitting a SYN/ACK packet to the client device. The SYN/ACK packetmay include a SYN cookie and identifying information for the networkdevice. The method may further include receiving an ACK packet from theclient device. The ACK packet may include the identifying informationfor the client device, identifying information for the network device,and the SYN cookie. The method may continue with establishing aconnection with the network for the client device.

Additional objects, advantages, and novel features will be set forth inpart in the detailed description section of this disclosure, whichfollows, and in part will become apparent to those skilled in the artupon examination of this specification and the accompanying drawings ormay be learned by production or operation of the example embodiments.The objects and advantages of the concepts may be realized and attainedby means of the methodologies, instrumentalities, and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not limitation, inthe figures of the accompanying drawings, in which like referencesindicate similar elements.

FIG. 1 is a network arrangement that provides network access control inaccordance with the present disclosure;

FIG. 2 is a signal flow diagram of a method for establishing a networkconnection between a client device and a network device;

FIGS. 3 and 4 collectively illustrate a flowchart of an exemplary methodfor network access control, used in some instances for protecting anetwork against a denial of service attack;

FIG. 5 is a block diagram of another exemplary network arraignmentsuitable for implementing one or more methods of the present disclosure;

FIG. 6 is a flowchart of a method of network access control;

FIG. 7 is a flowchart of another example method of network accesscontrol; and

FIG. 8 is a schematic diagram of an example computing system that can beused to implement the present technology.

DETAILED DESCRIPTION

While this technology is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail several specific embodiments with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the technology and is not intended to limit the technologyto the embodiments illustrated.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” or“according to one embodiment” (or other phrases having similar import)at various places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. Furthermore, depending on the context ofdiscussion herein, a singular term may include its plural forms and aplural term may include its singular form. Similarly, a hyphenated term(e.g., “on-demand”) may be occasionally interchangeably used with itsnon-hyphenated version (e.g., “on demand”), a capitalized entry (e.g.,“Software”) may be interchangeably used with its non-capitalized version(e.g., “software”), a plural term may be indicated with or without anapostrophe (e.g., PE's or PEs), and an italicized term (e.g., “N+1”) maybe interchangeably used with its non-italicized version (e.g., “N+1”).Such occasional interchangeable uses shall not be consideredinconsistent with each other.

It is noted at the outset that the terms “coupled,” “connected”,“connecting,” “electrically connected,” etc., are used interchangeablyherein to generally refer to the condition of beingelectrically/electronically connected. Similarly, a first entity isconsidered to be in “communication” with a second entity (or entities)when the first entity electrically sends and/or receives (whetherthrough wireline or wireless means) information signals (whethercontaining data information or non-data/control information) to thesecond entity regardless of the type (analog or digital) of thosesignals. It is further noted that various figures (including componentdiagrams) shown and discussed herein are for illustrative purpose only,and are not drawn to scale.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Embodiments disclosed herein may be implemented using a variety oftechnologies. For example, the methods described herein may beimplemented in software executing on a computer system or in hardwareutilizing either a combination of microprocessors or other speciallydesigned application-specific integrated circuits (ASICs), programmablelogic devices like FPGA's, or various combinations thereof. Inparticular, the methods described herein may be implemented by a seriesof computer-executable instructions residing on a storage medium such asa disk drive, or computer-readable medium. It should be noted thatmethods disclosed herein can be implemented by a computer, e.g., adesktop computer, server, tablet computer, laptop computer, smartphoneand so forth.

The present disclosure relates generally to data processing, morespecifically to security mechanisms that are employed by an ApplicationDelivery Controller (ADC) to prevent a denial of service attack.

Websites, web and mobile applications, cloud computing, and various weband mobile services have been rising in popularity. Some examples offast growing consumer services include smart phone applications,location based services, navigation services, e-book services, videoapplications, music applications, Internet television services, and soforth. Subsequently, more and more servers are deployed within datanetworks, including the Internet, to accommodate the increasingcomputing and data storage needs. These servers are typically arrangedin data centers or web farms, which may include ADCs, GSLB and/or serverload balancers (SLBs).

Conventionally, an ADC is a network device disposed in a datacenter andpart of an application delivery network (ADN). The ADC functions toperform common tasks, normally done by web servers, in an effort toremove some load from the web servers. ADCs are typically placed betweenthe firewall/router and the host (web) servers. In addition,conventional ADCs may include various features providing forcompression, caching, connection multiplexing, application layersecurity, and content switching. These features may be combined withbasic server load balancing, content manipulation, advanced routingstrategies, and highly configurable server health monitoring.

Additionally, ADCs may manage load balancing and delivery of servicesessions from client host computers to servers based at least in part onincoming service requests. As more servers are deployed, additional ADCsmay be deployed. Similarly, as more servers are pooled together withinthe data center or spread across multiple data centers to providescalability, ADCs may become bottlenecks slowing data transmissionsbetween peers on the network.

In TCP/IP networks, one method of establishing a connection between twonetwork devices such as a client device and a server, is through the useof a SYN packet, also sometimes referred to as a SYN flag, tosynchronize the sequence numbers of the two devices. In this scenario,the client device that wishes to establish the connection first sends aSYN packet from the client to the server. The SYN packet may compriseinformation within it such as the source IP address, source port,destination IP address, destination port, and a sequence number for theprotocol connection. The sequence number may be used by the TCP stack toreassemble the data stream. The first sequence number sent by a networkdevice initiating the communication may be any value as decided by thatoriginating network device.

In a typical TCP/IP stack, a SYN packet is sent from a client device toa server, in an attempt to establish a network connection with thatserver. Once the server receives the SYN packet, it typically respondswith a SYN/ACK to acknowledge receipt of the SYN packet and the requestto establish a connection. Upon receipt of the SYN/ACK, the clientdevice typically responds with an acknowledgement, ACK packet, and thenetwork connection is established. Until the server receives the finalACK packet from the client device, the connection is said to be in thehalf-open phase.

In a stateful TCP/IP stack, a server typically allocates resources to aparticular potential network connection when it receives the initial SYNpacket from the client device. When the ACK packet is received, theresource gets allocated to a different state. If a server receives alarge amount of SYN packets while in the half-open state, it may becomeoverwhelmed by the amount of resources necessary to respond to all ofthe SYN packets.

In a typical SYN attack, the server gets overwhelmed by SYN packetscoming in at a faster rate than it can process them. This may lead to adenial of service by the server, because the server is overwhelmed bythe sheer number of SYN packets it receives, such that it doesn't haveenough resources to respond to all of the requests, and thus is unableto respond to any of them.

There may also be other types of attacks on a server, such as a spoof.In this scenario, a SYN packet is sent from one device, but the IPaddress is spoofed, such that it appears to be coming from a differentdevice's IP address. In this scenario, when a SYN packet is sent by theclient device to the server, the server may respond with a typicalSYN/ACK to the client device from which it appears the message camefrom. Since the IP address was spoofed, the SYN/ACK message actuallyarrives at a different device than originally sent the SYN. Thus, theclient device that receives the SYN/ACK message may respond with a“reset” instruction since it did not send the original SYN packet and isnot interested in establishing a connection with the server at thattime.

Another type of attack that may occur on a server is a botnet attack. Inthis scenario, there may be attack software, such as a trojan, virus,malware, or any other unauthorized software (e.g., malware), installedon a client device. At periodic intervals, the attack software mayattempt to establish a connection between the client device that itresides on and the server, unbeknownst to the user of the client device.Since the IP address of the client device that is sending the SYN packetis a legitimate IP address, it will receive the SYN/ACK message, andrespond with an ACK packet to establish a proper connection. Once theconnection has been established, the unauthorized software on the clientdevice, may then attempt to overwhelm the server and cause it to shutdown, send it a virus, or implement any other type of unauthorizedsoftware to interfere with the server's operations.

In a typical TCP/IP stack, when a SYN packet is first received by aserver, it retains a copy of the SYN packet received, and allocatesresources to respond to the SYN packet. This is known as a statefulsolution. In a stateless solution, the server does not allocate anyresources until the connection is established.

To help protect against these types of attacks, a SYN-cookie may beplaced in a SYN/ACK packet. When a server receives a SYN packet whileoperating in a stateless mode, it can discard the SYN queue entry andtransmit a SYN/ACK response to the client in the form of a SYN-cookie.The data in the SYN-cookie may comprise a sequence number of the server,an acknowledgement of the original SYN request, and other information.When the client device receives this SYN-cookie and replies with an ACKpacket, that ACK packet may comprise the sequence number of the client,an acknowledgement of the SYN-cookie, and any other information. Whenthe server recognizes the proper acknowledgement of the SYN-cookie thatit sent, it can then confirm that the client device is trying toestablish a legitimate connection and the client's IP address has notbeen spoofed.

A SYN cookie may be an initial sequence number that is carefullyconstructed according to various rules, including a slowly incrementingtimestamp, a maximum segment size value, a cryptographic hash functioncomputed over a network device's IP address and port number, theclient's IP address and port number, and the timestamp, or any othervalue or combination thereof.

The present technology provides various systems and methods foroperation of a service on a network. It provides technology to identifybotnets, trojans, viruses, malware, and other type of unauthorizedservices from accessing and overwhelming a network device providing aservice. These systems and methods may be utilized to prevent a denialof service attack.

The present technology may be implemented on a network device in a datanetwork such as the Internet including a plurality of switches, routers,virtual switches, web farms, host servers, and other units. The presenttechnology provides enhanced performance and security of a networkdevice such as an Application Delivery Controller (ADC) and allowsimplementing scalable business solutions for any services, applications,clouds and organizations. Furthermore, the present technology provides ascalable, high-performance application networking platform, which candeliver superior reliability, security, and energy efficiency at lowertotal cost of ownership. ADC can also provide increased infrastructureefficiency, a faster end user experience, comprehensive Layer 4-7feature set and flexible virtualization technologies such as VirtualChassis System, multi-tenancy, and more for public, private and hybridcloud environments. The network devices may include software and/orhardware components/platforms that may vary depending on a particularapplication, performance, infrastructure, network capacity, data trafficparameters, and so forth. A more detailed explanation of an exemplarymethod of ADC operation is described in U.S. utility patent applicationSer. No. 13/791,760, filed on Mar. 8, 2013, titled “Application DeliveryController and Global Server Load Balancer” which is incorporated hereinby reference in its entirety.

Turning now to FIG. 1, a high-level block diagram of an exemplarysymmetric network topology 100 suitable for implementing one or moremethods of the present disclosure is shown. The network topology 100shown by FIG. 1 may include a number of host servers 105A-N, a number ofswitches, such as switch 110A and switch 110B combining/coupling thehost servers 105A-N and thus performing Layer 2 aggregation andcorresponding switching. The topology 100 may further include an ADC 115including one (or more) ADC switches, such as ADC switch 120A and ADCswitch 120B. The ADC switches may operate in different modes, such asstandalone, active/standby mode, active-Active and others.

The topology 100 may further include a communications network 125, whichmay refer to, for example, the Internet, Local Area Network (LAN), WideArea Network (WAN), Internet, a cellular network, a telephone network,or any other switched network or their combinations. There is also aplurality of clients 130A-N, which may include end user computers,mobile phones, thin clients, and so forth. There are also one or moreLocal DNS Servers 140A-N which may be associated with one or moreclients 130A-N and/or one or more host servers 105A-N. As shown in FIG.1, the topology may include a GSLB 135, which may employ one or more ofthe methods disclosed herein.

Generally speaking, load balancing is a technique that may be used fordistributing the workload evenly across clients, networks, host servers,and other networked resources. The load balancing may enhanceutilization of resources and enable maximize throughput with minimumresponse time, hence avoiding overloading of a single server. GlobalServer Load Balancing (GSLB) is an extension of the load balancing. Withthis technology, network traffic is among different web farms, datacenters, and host servers located at different geographical locations.This technology may be highly efficient in avoiding local downtimes andremote downtimes. Furthermore, as will be appreciated by those skilledin the art, ADC 115 may act as a master to monitor “health” andresponsiveness of other sites hosted by the host servers 105A-N. A GSLB135 may be configured to redirect service requests to other nearby hostservers if one of the host servers does not respond timely. For example,the GSLB 135 may redirect service requests from client 130A for aservice from host server 105A to host server 105B if client 130Aexperiences deleterious performance issues such as latency issues causedby host server 105A underperformance.

Furthermore, this technique may allow forwarding visitor requests to ahost server located most closely geographically to the place from wherethe request sent. In addition, if a traffic threshold is reached at themost geographically proximate host server, the service requests may beforwarded to other host servers located at a different geographicallocation.

As will be appreciated by those skilled in the art, an ADC switch, suchas ADC switch 120A may operate in an active mode, backup mode, or someother modes depending on an application. The ADC switches 120A and 120Bprovide redundancy protection and failover protection for selectednetworks or parts of the network 125. The ADC switches 120A and 120Balso report their status (i.e., current operating mode) to selectednetwork elements or other switches 110A and/or 110B, for example.

FIG. 2 illustrates a method of operation for a network device, such asADC 115, host servers 105A-N, switches 120A-B. The network device isconfigured to provide network security operations. Broadly described,components of the network 125 use various SYN packet/cookie processes toeffectuate security operations. In an example, the client device 130Amay be required to transmit a SYN packet prior to registration on thenetwork. Thus, to access a service on the network the client device 130Awill transmit to the network a SYN packet. The composition of the SYNpacket may be any single or composition of characteristics such as asequence number, an IP address, a MAC (Media Access Control) address,IMEI (International Mobile Equipment Identity), SSID (Service SetIdentifier), a source port, or any other identifying characteristic thatcan be used to identify a device on a network.

The network device, such as the ADC 115, may receive a SYN packet from aclient device 130A to initiate a network connection in step 205. Oncereceived, the network device may perform a SYN packet analysis in step210. Various methods may be used in the SYN packet analysis.

For example, the network device may then use a lookup table in step 210to determine whether the client device 130A is already on a white listof trusted devices, or a black list of untrusted devices. The lookuptable is in a database, or any other data structure. The lookup tablemay be stored on computer readable medium on the network device, or in aremote location accessible by the network device. The white list andblack list of trusted devices and untrusted devices are recorded in eachrespective list by source IP address, source port, or any otheridentifying characteristic in the received SYN packet from the clientdevice 130A. The white list and black list are created and administeredby a network administrator, and may be periodically updated. The whitelist and black list may also incorporate various network policiesdeployed by the network administrator.

If the client device 130A is found on a black list of devices, SYNpackets received from the client device 130A are dropped. That is, theclient device 130A is not allowed access to the network.

If the client device 130A that is wishing to initiate the networkconnection is not found in step 210 on either the white list or theblack list, then the network device may send a SYN/ACK message with aSYN-cookie to the client device 130A in step 215. The SYN-cookie maycomprise a sequence number that identifies the network device, an ACKnumber acknowledging the sequence number from the SYN packet, and/or anyother identifying information that is representative of the networkdevice. The SYN cookie is stored on the client device 130A.

In exemplary embodiments, an original SYN packet from a client device130A may have a sequence number (or other identifying information) thatrepresents the client device 130A. A SYN/ACK packet is returned to theclient device 130A from the network device. This SYN/ACK messagecomprises the client's sequence number (as found in the original SYNpacket) plus one, and a sequence number that identifies the networkdevice. An ACK packet/message is subsequently returned by the clientdevice 130A in step 220 to confirm the connection. The ACK packet maycomprise the sequence number for the network device network device plusone. The network device verifies the information in the ACK message instep 225 and establishes the network connection in step 230.

FIGS. 3 and 4 illustrate embodiments of a method where a networkadministrator may optionally choose to enable a SYN-cookie tolerancelevel and other optional features. Generally, the process is initiatedas above, with the network device receiving a SYN packet from the clientdevice in block 305. Next, the network device looks up the client deviceas identified in the SYN packet in block 310. If the device is on ablacklist, the SYN packets are dropped in block 315. If the device isnot found in a black or white list the network device returns a SYN/ACKmessage in block 320.

In the event that the client device is on a white list or has beentransmitted a SYN/ACK message by the network device, the network devicemay execute a SYN-cookie tolerance analysis in block 325. In general, aSYN-cookie tolerance level may specify a certain number of times that aclient device can fail to return the proper sequence numbers in aSYN-cookie before the client is added to the black list in block 340.

If the client device 130A is already on the white list of trustedsources, then the network device may check whether a SYN-cookietolerance level for the particular client device 130A has been enabled.It will be understood that there are a number of reasons why a clientdevice may return an improper SYN-cookie in its ACK packet to thenetwork device, such as a networking delay, hardware issues, and soforth. Thus, in some embodiments, the network administrator may have theoption of enabling a SYN-cookie tolerance threshold that may specify thenumber of times a client device must fail to return the matching SYNcookie before the client device is added to the black list in block 340.

If the SYN-cookie tolerance feature is enabled, then the network devicemay send the client device 130A a SYN/ACK with a SYN cookie. If the SYNcookie tolerance level is not enabled, then the network device may checkwhether the client device 130A has exceeded a connection rate/limitpolicy in block 345. A connection rate/limit policy connectionrate/limit policy may define a number of times a client device 130A mayattempt to connect to the network device in a given time period. Theconnection rate/limit policy may check one or more characteristics ofthe client device, such as source IP address, source port, timestamp, orany other characteristic. The specific characteristics that are checkedmay be configurable by a network administrator, or are predetermined bythe network device.

If the client device has exceeded the allowable connection rate/limitpolicy, then the network device may either simply drop the packet atblock 315 and not allow the network connection to be established, or itmay add the client device to the black list of untrusted sources inblock 340. This determination is, in one embodiment, based on which ofthe one or more source characteristics have exceeded the allowable ratelimit (i.e., source port, IP address, wrong timestamp, and so forth.).Exceeding the allowable connection rate/limit policy may indicate to thenetwork device that the client device may be a botnet, or any other typeof unauthorized program that may be attempting to overwhelm the networkdevice and cause it to stop functioning properly. If the client devicehas exceeded an allowable rate limit and the SYN packet is dropped bythe network device in block 315 and no reply is sent to the clientdevice.

In various embodiments, a determination is whether the client device hasexceeded a connection rate/limit policy despite being on the white listsince the client device may still be a spoof. In a spoof attack, thesource IP address may be rotated, but the source port may remain thesame. For example, a client device may use an IP address of 123.12.12.1with a port of :80 in a first instance, and a second IP address132.34.34.2 with a port of :80 in a second instance.

Thus, querying the number of times a source IP address has attempted toconnect to the network device will yield a different result thanquerying the number of times a source port has attempted to connect tothe network device. Therefore, despite being on the white list fortrusted sources, the client device may still need to be authenticated bychecking the connection rate/limit policy for other characteristics ofthe client device.

If the connection rate/limit policy(s) has been exceeded for a clientdevice, then the client device may be added to the black list ofuntrusted sources in block 340. In some embodiments, an unauthorizedsource may attempt to connect to the network device via constantlyguessing a SYN-cookie. In this embodiment, the network device may deploya check on the rate limit of SYN-cookies received from a particularclient in block 345.

If a rate limit or number of SYN-cookies received from a particularsource has exceeded a threshold, the SYN packet from the client devicemay be dropped in block 315. If the rate limit or number of SYN-cookieshas not exceeded the threshold, the network device may reply with aSYN-cookie reply ACK in block 355 to begin the network connection. Theparticular rate limit or number of SYN-cookies that are authorized froma client device may be preset by the network device, or configurable bya network administrator. Additionally, the allowable threshold may bevariable based on any characteristic in the SYN packet, such asgeographic region, timestamp, source IP address, source port,destination IP address, destination port, and so forth. For example, ifthe client device is located in a geographical region known fororiginating malware or fraudster activity, the network administrator mayset the rate limit or number of SYN-cookies for that area lower than amore trusted geographical location.

If the connection rate/limit policy has not been exceeded, then anetwork connection is established between the client device and thenetwork device in block 360, and packets from the client device mayenter the flow process for the network.

After receiving a SYN/ACK, when a client returns the ACK packet in block405, a determination may occur as to whether the particular flow hasalready been observed in block 410. The determination is based on thesequence numbers in the ACK packet and SYN-cookie, or any othercharacteristic or combinations thereof.

If the flow was previously observed by the network device, then thepacket from the client device may enter the flow process for thenetwork, in block 415. That is, the client device is permitted to usethe network connection. If the flow has not been previously observed bythe network device, then the SYN-cookie returned by the client devicewith the ACK packet may be checked by the network device in block 420.If the SYN-cookie is determined to be correct and the SYN-cookie checkpasses, then the client device is added to the white list in block 425,even if the client device was previously on the black list. The networkconnection is reset between the network device and client device inblock 430.

If the SYN-cookie check fails, then the network device may determinewhether an optional SYN-cookie tolerance level has been enabled in block435. If not, then the client device may be added to the black list inblock 440 and the packet may be dropped by the network device in block455 such that no return message is sent to the client device and noconnection is established. If a SYN-cookie tolerance level is enabled,then the SYN-cookie threshold may be decreased by one in block 445.Since the client has failed to return the proper SYN-cookie, thethreshold level is decreased. For example, if the initial SYN-cookietolerance level is five attempts, the first time the client device failsto return the proper SYN-cookie, the tolerance level may be decreased byone such that four attempts are remaining. Each improper SYN-cookiereturn results in a decrease of the tolerance level in an iterativefashion, until the threshold reaches zero in block 450 such that no moreattempts remain. If the threshold has reached zero, then the clientdevice is to the black list and the packet may be dropped by the networkdevice in block 455.

The SYN-cookie check and SYN-cookie tolerance may be employed in variousembodiments to prevent an ACK attack. An ACK attack may occur when aclient device repeatedly sends ACK packets to a network device bycontinually attempting to reconstruct the SYN-cookie. Thus, in certainembodiments, it may be beneficial to limit the number of ACK packets thenetwork device may receive from a client device that do not pass theSYN-cookie check.

FIG. 5 illustrates a block diagram of an exemplary network topology 500operating in an “Asymmetric” mode, also sometimes known as “DirectServer Return” mode. In this mode, a client 530A may submit a requestfor services. The request is transmitted through the communicationsnetwork 525 to the ADC 515. Once the ADC 515 can verify that the clientis a trusted source and the request is legitimate using a SYN-cookie orany other verification method, the ADC 515 may forward the request toone or more host servers 505. The one or more host servers 505 may thenreturn the response data directly to the client 530A. Typically, theflow of traffic from the host servers 505 to the client 530A is greaterthan the flow of traffic from the client 530A to the host servers 505.Thus, by monitoring the traffic in both directions, the ADC 515 maybecome a bottleneck in the network, since it may not be able to processsuch large volumes of traffic. By sending the response data directlyfrom the host servers 505 to the client 530A, the ADC 515 has lesstraffic to process, and is less likely to slow down the flow of trafficin the network.

The above described systems and methods are implemented on a networkdevice positioned in a symmetric (FIG. 1) or asymmetric network topology(FIG. 5). A symmetric network topology may place the network device inline with the flow of traffic between the server and client device, suchthat all communications between the server and client device passthrough the network device. In an asymmetric network topology (FIG. 5),a different path is used for traffic flowing to and from the server,such that the network device placed between the client and server mayonly see the traffic flow in one direction.

In certain embodiments, the above described methods and system mayoperate in a stateless mode. In a stateless mode, the network devicedoes not retain a record of previous interactions, and thus eachinteraction and request by the client device is handled based oninformation that is received with the request. Through the use of theSYN-cookie, the network device may have enough information to evaluateand authenticate the client device without retaining information aboutthe prior SYN packet received from the client device.

Though the above described methods and systems for operation of networkdevices have been described for preventing attacks on a network deviceby instituting rate limits in the context of SYN packets on an TCP/IPnetwork, similar methods and systems may also be applied on other typesof networks, including a UDP network. For example, a network device on aUDP network may also determine whether a source rate limit has beenexceeded, or institute other metrics or network key performanceindicators (KPI).

FIG. 6 is a method for network access control. The method includesreceiving at a network device a SYN packet from a client device over anetwork, in step 605. As mentioned above, the SYN packet comprisesidentifying information for the client device. Next, the method includesdetermining if the client device is a trusted source for the networkusing the SYN packet in step 610. Many different methods may be used todetermine if the client device is trusted, such as using a determiningif the client device is on a black or white list, determining if theclient device has transmitted to the network device a number of ACKpackets that include an incorrect SYN cookie, determining if clientdevice has violated an allowable connection rate policy, and/ordetermining if the client device has exceeded an allowable rate limit ofSYN cookies, as well as other methods described herein.

If the client device is a trusted resource, the method further includesreceiving an acknowledgement (ACK) packet from the client device thatincludes identifying information for the client device and identifyinginformation for the network device, in step 615. Next, the methodincludes establishing a connection with the network for the clientdevice, in step 620. If the client device is determined not to be atrusted device, the method may include dropping the SYN packet to denynetwork access to the client device, in step 625.

FIG. 7 is a flowchart of a method for providing network access. Themethod may include determining, in step 705, if a client device is atrusted source for the network using the SYN packet. In general, the SYNpacket comprises identifying information for the client device such asan IP address, a port, a MAC address or other identifying information.

This information can be searched against a database that includes blackand white lists of device identifiers that are known to be untrustedsources (black list) or trusted sources (white list). If the system isunable to determine from the SYN information if the client device istrusted or untrusted, the method includes transmitting a SYN/ACK packetto the client device, in step 710. In some embodiments, the SYN/ACKpacket comprises: (a) identifying information for the client device plusan additional value; (b) a SYN cookie, and (c) identifying informationfor the network device.

Next, the method comprises the network device receiving an ACK packetfrom the client device to confirm the establishment of a networkconnection between the network device and the client device in step 715.If the ACK packet is received, the method includes establishing, at step720, a connection with the network for the client device.

During network sessions, the method may include placing the clientdevice on a black list if the client device is subsequently determinedto be an untrusted resource. For example, the client device may use anincorrect SYN cookie a certain number of times. In another example, theclient device may violate an allowable connection rate policy or may befound to create a network packet flow has been not been previouslyobserved within the network. Any of these examples may indicate that theclient device is acting maliciously on the network. In these instances,the client device can be placed onto a black list and its future networkpackets dropped so as to prevent the establishment of a networkconnection for the client device with the network.

FIG. 8 illustrates an exemplary computing system 1 that is to implementan embodiment of the present systems and methods. The computing system 1of FIG. 8 may be implemented in the contexts of the likes of the server105 described herein. The computing system 1 of FIG. 8 includes aprocessor 10 and main memory 20. Main memory 20 stores, in part,instructions and data for execution by processor 10. Main memory 20 maystore the executable code when in operation. The computing system 1 ofFIG. 8 further includes a mass storage device 30, portable storagedevice 40, output devices 50, user input devices 60, a display system70, and peripherals 80.

The components shown in FIG. 8 are depicted as being connected via asingle bus 90. The components may be connected through one or more datatransport means. Processor 10 and main memory 20 may be connected via alocal microprocessor bus, and the mass storage device 30, peripherals80, portable storage device 40, and display system 70 may be connectedvia one or more input/output (I/O) buses.

Mass storage device 30, which may be implemented with a magnetic diskdrive or an optical disk drive, is a non-volatile storage device forstoring data and instructions for use by processor 10. Mass storagedevice 30 can store the system software for implementing embodiments ofthe present technology for purposes of loading that software into mainmemory 20.

Portable storage device 40 operates in conjunction with a portablenon-volatile storage medium, such as a floppy disk, compact disk ordigital video disc, to input and output data and code to and from thecomputing system 1 of FIG. 8. The system software for implementingembodiments of the present technology may be stored on such a portablemedium and input to the computing system 1 via the portable storagedevice 40.

Input devices 60 provide a portion of a user interface. Input devices 60may include an alphanumeric keypad, such as a keyboard, for inputtingalphanumeric and other information, or a pointing device, such as amouse, a trackball, stylus, or cursor direction keys, or a scanner forreading bar codes. Additionally, the computing system 1 as shown in FIG.8 includes output devices 50. Suitable output devices include speakers,label and receipt printers, network interfaces, and monitors.

Display system 70 may include a liquid crystal display (LCD) or othersuitable display device. Display system 70 receives textual andgraphical information, and processes the information for output to thedisplay device.

Peripherals 80 may include any type of computer support device to addadditional functionality to the computing system. Peripherals 80 mayinclude a modem or a router.

The components contained in the computing system 1 of FIG. 8 are thosetypically found in computing systems that may be suitable for use withembodiments of the present technology and are intended to represent abroad category of such computer components that are well known in theart. Thus, the computing system 1 can be a personal computer, hand heldcomputing system, telephone, mobile computing system, workstation,server, minicomputer, mainframe computer, or any other computing system.The computer can also include different bus configurations, networkedplatforms, multi-processor platforms, etc. Various operating systems canbe used including UNIX, Linux, Windows, Macintosh OS, Palm OS, and othersuitable operating systems.

Some of the above-described functions may be composed of instructionsthat are stored on storage media (e.g., computer-readable medium). Theinstructions may be retrieved and executed by the processor. Someexamples of storage media are memory devices, tapes, disks, and thelike. The instructions are operational when executed by the processor todirect the processor to operate in accord with the technology. Thoseskilled in the art are familiar with instructions, processor(s), andstorage media.

It is noteworthy that any hardware platform suitable for performing theprocessing described herein is suitable for use with the technology. Theterms “computer-readable storage medium” and “computer-readable storagemedia” as used herein refer to any medium or media that participate inproviding instructions to a CPU for execution. Such media can take manyforms, including, but not limited to, non-volatile media, volatile mediaand transmission media. Non-volatile media include, for example, opticalor magnetic disks, such as a fixed disk. Volatile media include dynamicmemory, such as system RAM. Transmission media include coaxial cables,copper wire and fiber optics, among others, including the wires thatcomprise one embodiment of a bus. Transmission media can also take theform of acoustic or light waves, such as those generated during radiofrequency (RF) and infrared (IR) data communications. Common forms ofcomputer-readable media include, for example, a floppy disk, a flexibledisk, a hard disk, magnetic tape, any other magnetic medium, a CD-ROMdisk, digital video disk (DVD), any other optical medium, any otherphysical medium with patterns of marks or holes, a RAM, a PROM, anEPROM, an EEPROM, a FLASHEPROM, any other memory chip or data exchangeadapter, a carrier wave, or any other medium from which a computer canread.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to a CPU for execution. Abus carries the data to system RAM, from which a CPU retrieves andexecutes the instructions. The instructions received by system RAM canoptionally be stored on a fixed disk either before or after execution bya CPU.

Computer program code for carrying out operations for aspects of thepresent technology may be written in any combination of one or moreprogramming languages, including an object-oriented programming languagesuch as Java, PHP, MySQL, HTML, Java Script, CSS, Smalltalk, C++ or thelike and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The program codemay execute entirely on the user's computer, partly on the user'scomputer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present technology has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Exemplaryembodiments were chosen and described in order to best explain theprinciples of the present technology and its practical application, andto enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

Aspects of the present technology are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general-purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

While the present invention has been described in connection with aseries of preferred embodiment, these descriptions are not intended tolimit the scope of the invention to the particular forms set forthherein. It will be further understood that the methods of the inventionare not necessarily limited to the discrete steps or the order of thesteps described. To the contrary, the present descriptions are intendedto cover such alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims and otherwise appreciated by one of ordinary skill inthe art.

What is claimed is:
 1. A system for network access control, systemcomprising: a network device comprising one or more processors; and amemory communicatively coupled to the network device, the memory storinginstructions executable by the one or more processors of the networkdevice, the network device being configured to: determine whether aclient device is a trusted source or an untrusted source for a networkusing a SYN packet received from the client device, the SYN packetcomprising identifying information for the client device; based on thedetermination that the client device is neither the trusted source northe untrusted source, transmit a SYN/ACK packet to the client device,the SYN/ACK packet comprising a SYN cookie and identifying informationfor the network device; receive an ACK packet from the client device,the ACK packet including the identifying information for the clientdevice, identifying information for the network device, and the SYNcookie; and establish a connection with the network for the clientdevice.
 2. The system of claim 1, wherein the network device is furtherconfigured to place the client device on a black list if the clientdevice is subsequently determined to be the untrusted source.
 3. Thesystem of claim 1, wherein the network device is further configured todrop, based on determining that the client device is the untrustedsource, the SYN packet to deny network access to the client device. 4.The system of claim 1, wherein the network device is further configuredto transmit, based on determining that the client device is the trustedsource, a SYN/ACK packet to the client device, the SYN/ACK packetcomprising identifying information for the network device; receive anACK packet from the client device that includes the identifyinginformation for the client device and the identifying information forthe network device; and establish the connection with the network forthe client device.
 5. The system of claim 1, wherein the network deviceis further configured to apply a SYN cookie tolerance level to determinewhether a number of times the client device provided an incorrect SYNcookie in one or more ACK packets when attempting to connect to thenetwork device exceeds a predetermined threshold, wherein the connectionis established when the number of times the client device provides theincorrect SYN cookie is below the predetermined threshold.
 6. The systemaccording to claim 1, wherein the SYN cookie comprises one or more ofthe following: a maximum segment size value and a cryptographic hashfunction computed using at least one of an IP address of the networkdevice, a port number of the network device, an IP address of the clientdevice, and a port number of the client device.
 7. The system accordingto claim 1, wherein the network device is further configured to: receivea number of ACK packets from the client device that include an incorrectSYN cookie, wherein the incorrect SYN cookie comprises identifyinginformation for the client device that is incorrect or identifyinginformation for the network device that is incorrect; apply a SYN cookietolerance level, wherein the SYN cookie tolerance level specifies anumber of times the client device is allowed to supply the incorrect SYNcookie; add the identifying information for the client device to a blacklist if the client device exceeds the SYN cookie tolerance level, theblack list storing identifying information for one or more untrustedsources; and drop subsequent SYN packets or ACK packets received fromthe client device.
 8. The system according to claim 1, wherein thenetwork device is further configured to: set an allowable connectionrate policy for the client device, wherein the allowable connection ratepolicy specifies a maximum number of times the client device is toattempt to connect to the network in a given time period; add theidentifying information for the client device to a black list if theclient device violates the allowable connection rate policy; and dropsubsequent SYN packets or ACK packets received from the client device.9. The system according to claim 1, wherein the network device isfurther configured to perform a SYN cookie check, the SYN cookie checkcomprising comparing information in the SYN cookie received in the ACKpacket from the client device with information in the SYN cookieprovided by the network device in the SYN/ACK packet, wherein theestablishing of the connection is performed based on passing, by theclient device, the SYN cookie check.
 10. A method for network accesscontrol, the method comprising: determining, at a network device,whether a client device is a trusted source or an untrusted source for anetwork using a SYN packet received from the client device, the SYNpacket comprising identifying information for the client device; basedon determining that the client device is neither the trusted source northe untrusted source, transmitting a SYN/ACK packet to the clientdevice, the SYN/ACK packet comprising a SYN cookie and identifyinginformation for the network device; receiving an ACK packet from theclient device, the ACK packet including the identifying information forthe client device, identifying information for the network device, andthe SYN cookie; and establishing a connection with the network for theclient device.
 11. The method of claim 10, further comprising placingthe client device on a black list if the client device is subsequentlydetermined to be the untrusted source.
 12. The method of claim 10,further comprising dropping, based on determining that the client deviceis the untrusted source, the SYN packet to deny network access to theclient device.
 13. The method of claim 10, further comprising: based ondetermining that the client device is the trusted source, transmitting aSYN/ACK packet to the client device, the SYN/ACK packet comprisingidentifying information for the network device; receiving an ACK packetfrom the client device that includes the identifying information for theclient device and the identifying information for the network device;and establishing the connection with the network for the client device.14. The method of claim 10, wherein the establishing the connectioncomprises connecting the client device to a host server such thatnetwork traffic flows directly from the host server to the clientdevice.
 15. The method of claim 10, further applying a SYN cookietolerance level to determine whether a number of times the client deviceprovided an incorrect SYN cookie in one or more ACK packets whenattempting to connect to the network device exceeds a predeterminedthreshold, wherein the connection is established when the number oftimes the client device provides the incorrect SYN cookie is below thepredetermined threshold.
 16. The method according to claim 10, furthercomprising: receiving a number of ACK packets from the client devicethat include an incorrect SYN cookie, wherein the incorrect SYN cookiecomprises identifying information for the client device that isincorrect or identifying information for the network device that isincorrect; applying a SYN cookie tolerance level, wherein the SYN cookietolerance level specifies a number of times the client device is allowedto supply the incorrect SYN cookie; adding the identifying informationfor the client device to a black list if the client device exceeds theSYN cookie tolerance level, the black list storing identifyinginformation for one or more untrusted sources; and dropping subsequentSYN packets or ACK packets received from the client device.
 17. Themethod according to claim 10, further comprising: setting an allowableconnection rate policy for the client device, wherein the allowableconnection rate policy specifies a maximum number of times the clientdevice is to attempt connecting to the network in a given time period;adding the identifying information for the client device to a black listif the client device violates the allowable connection rate policy; anddropping subsequent SYN packets or ACK packets received from the clientdevice.
 18. The method according to claim 10, further comprising:performing a SYN cookie check, the SYN cookie check comprising comparinginformation in the SYN cookie received in the ACK packet from the clientdevice with information in the SYN cookie provided by the network devicein the SYN/ACK packet, wherein the establishing of the connection isperformed based on passing, by the client device, the SYN cookie check.19. The method according to claim 10, further comprising: setting a SYNcookie threshold, wherein the SYN cookie threshold identifies a totalnumber of times the client device is to provide the SYN cookie to thenetwork device; for each time the client device provides the SYN cookieto the network device, reducing the SYN cookie threshold by one untilthe SYN cookie threshold is zero; when the SYN cookie threshold is zero,adding the identifying information for the client device to a blacklist; and dropping subsequent SYN packets or ACK packets received fromthe client device.
 20. A non-transitory computer-readable storage mediumhaving embodied thereon a program executable by at least one processorto perform a method for network access control, the method comprising:determining, at a network device, whether a client device is a trustedsource or an untrusted source for a network using a SYN packet receivedfrom the client device, the SYN packet comprising identifyinginformation for the client device; based on determining that the clientdevice is neither the trusted source nor the untrusted source,transmitting a SYN/ACK packet to the client device, the SYN/ACK packetcomprising a SYN cookie and identifying information for the networkdevice; receiving an ACK packet from the client device, the ACK packetincluding the identifying information for the client device, identifyinginformation for the network device, and the SYN cookie; and establishinga connection with the network for the client device.